Dowells and Native American heritage

George Dowell Polly Tomberlin (Cherokee Blood)

According to family Bible records my ancestors are George Dowell (b.1789 - d.?) and Polly Tomberlin (b. abt. 1798 - d. ?)Family tradition says that Polly Tomberlin had Cherokee Indian blood, but the amount is unknown. George and Polly Dowell had the following children: Patsy Emeline b.1813; Rebecca Elizabeth b.1815; John Allen b. 1817; Eliza Jane b.1820; George Martin b. 1822 in Ogrash Valley, Alabama; Mary White b.1824; Reuben Hickman b.1826; Keziah Elvira b.1828; Nancy Caroline b. 1830; and Priscilla America b. 1832. My g grandfather is George Martin Dowell who married Elizabeth Catherine Knight (b.ca 1832 perhaps in Wales or England)circa 1845 probably in Muscatine, Iowa. George Martin Dowell and Elizabeth Knight had a son Alonzo Henry Dowell (b. 1847 in Fairport, Muscactine,Iowa. Alonzo married Rosamond De Moss (b. 1852)in 1867 in Fairport, Muscatine, Iowa. Alonzo and Rosamond are my g grandparents and both died in Stroud, Lincoln Co. OK in 1929 and 1933 respectively. Does anyone have information on these Dowells particularly on who the parents of George Dowell and Polly Tomberlin were? Also does the location of "Ogrash Valley" in Alabama sound familiar to anyone? Any help would be much appreciated.